Rusty or Brown Hot Water

Step 1: Hot only, or hot and cold?

This one test sorts out most cases. Run a cold tap, then a hot tap, into white cups or a white bucket.

• Only the hot is brown: the water heater is the likely source. Keep reading.
• Both hot and cold are brown: the problem is upstream of the heater. On a well, that's usually iron in the water; see iron in well water. On city water, call the utility, since main breaks and hydrant flushing stir up rust.
• Brown only at first, then clears: often old galvanized steel pipes rusting inside, which shows worst after water sits overnight.

Step 2: Drain a sample from the tank

Turn off the heater, let it cool, then put a bucket under the drain valve near the bottom and open it briefly. Look at what comes out.

• Rusty water, then clear: sediment and rust flakes have settled in the bottom. A full flush may help for a while.
• Rusty the whole time: the tank is likely corroding inside.
• Sand or white grit: that's mineral sediment, not rust. It's a different problem, covered on our noises page.

The drain valve on many tanks is plastic and clogs easily with sediment. If it won't flow, don't force it. A.O. Smith says to call a plumber when sediment blocks the drain.

What's causing it

A spent anode rod

Every glass-lined steel tank has an anode rod, a metal rod that corrodes on purpose so the tank doesn't. Once it's gone, the tank starts to rust instead. A.O. Smith says a deteriorating anode speeds up corrosion and recommends checking it every year. They also say anodes usually last about 5 years, sooner in some water.

If you catch it early, a new anode can slow the damage. Pull the old one: if you see bare steel wire with little metal left on it, it's done. Our water heater anode rod page covers how to check and replace it.

Corrosion inside the tank

Once the steel itself is rusting, a new anode won't undo it. The tell is rust color that doesn't clear after a flush, often along with rust around the top fittings or at the base. Rheem says water pooling at the base often indicates internal corrosion, and that once a tank deteriorates from the inside, replacement becomes the only safe and cost-effective solution.

Rusty fittings and nipples

Sometimes the rust comes from the steel nipples where the pipes connect on top of the tank, not from the tank. Look for rust and crust around the hot outlet. Dielectric nipples and unions can corrode where copper meets steel. A plumber can swap them without replacing the heater.

Iron bacteria or iron in the water

On well water, iron and iron bacteria can stain hot water reddish brown, and hot water often shows it more. Vermont's health department notes that bacterial slime can be reddish-brown when iron bacteria are involved, and that sulfur bacteria can promote iron bacteria growth. If your water also smells, read hot water smells like rotten eggs.

What to do about it

1. Flush the tank. It clears sediment buildup and gives you a clean baseline. See how to flush a water heater.
2. Check or replace the anode rod, especially on a tank more than a few years old.
3. Check the fittings on top for rust and replace any corroded nipples.
4. Watch the base and the drain pan. Any weeping from the tank body means it's time to replace.
5. Test your well water if the cold side is discolored too.

Is rusty water safe? Rust itself is mostly a staining and taste problem, but brown water can carry sediment and bacteria, so don't drink it until you know the source. If you're on a well, a test from a state-certified lab tells you what's actually in it.

When to call a plumber, and what it costs

Call if the tank is leaking, if the anode is seized, or if rust keeps coming back after a flush and a new anode. HomeGuide's numbers:

HomeGuide says water leaking from the bottom of the tank usually means the heater needs replacing, and suggests replacement once a heater is over ten years old. A rusty tank of that age is near the end. Price a new one on water heater cost before you spend on parts.